From Dota 2 Wiki
Trading can be done between players through the Steam interface. Most cosmetic items are tradeable.
Untradable items... further results
Trade restrictions are identical to Market restrictions.
- Items of certain quality are not tradeable.
- Items unboxed from a Treasure cannot be traded until three months after the treasure was released.
- This does not apply to Very Rare drops.
- Items purchased from the Market cannot be traded or sold again on the Market within 1 week of purchase.
- Account must have a successful purchase older than thirty days, but not older than a year.
- Account must have had Steam Guard enabled for 15 days.
- If you have had your password reset by Steam Support you will need to wait another 15 days with Steam Guard enabled before you can trade or list items on the Community Market.
- If a chargeback has occurred on your account you will be eligible 30 days after your next successful purchase.
- If a password is reset on an active account, trading will be restricted for 5 days. If an account has not been active within the past two months, this restriction will last for 30 days. this does not affect password changes, only password resets.
- Adding a new purchase method to an account will trigger a trade and market restriction for 7 days.
- Accounts under trade or VAC bans cannot trade or use the market.